1. Field of the Invention
This invention generally relates to an imaging system using a multiple of light beams, such as a color imaging system, and, in particular, to a method and system for stabilizing the light intensity of each of a plurality of light beams used for imaging. More specifically, the present invention relates to an imaging system and method using a multiple of light beams emitted from one or more semiconductor lasers, whereby the light intensity of each of the multiple of light beams is stabilized uniformly.
2. Description of the Prior Art
An imaging system using a plurality of light beams is well known and it is typical in the field of a multiple color imaging system, such as a color copier. Such an imaging system using a plurality of light beams typically includes a plurality of semiconductor lasers as the source of each of the light beams. However, as the characteristic of the semiconductor laser varies depending on the surrounding temperature, there is usually provided a stabilizing feed-back loop for keeping the characteristic of the semiconductor laser stabilized, thereby preventing the light intensity of the light beam emitted from the semiconductor laser from being adversely affected by the changes in the surrounding temperature. However, in accordance with the prior art, such a stabilizing feed-back loop is usually provided independently for each of the semiconductor lasers. Since the characteristic sometimes differs from one semiconductor laser to another, the prior art stabilizing technique is often not sufficient in obtaining an image of high quality. Particularly, in the case of a color copier, different color component images of the same original image are exposed to the same or a plurality of photosensitive members, so that if there is a difference in light intensity between the different color component images, the resulting image would not be a faithful reproduction of the original image.
Referring now to FIG. 3, a typical scheme of stabilizing the output of a single semiconductor laser having a stabilizing feed-back loop is shown. As shown, a laser driver circuit 1 modulates a driving current to be applied to a semiconductor laser 2 in accordance with a video data signal supplied thereto. The semiconductor laser 2 receives the driving current modulated with video information and emits a light beam 3 in response thereto. The light beam 3 thus emitted is directed towards an imaging member, such as a photosensitive member, on which an electrostatic latent image corresponding to the video information is formed. As shown in FIG. 3, the light beam 3 emitted from the semiconductor layer 2 is partially reflected by a beam splitter 4, and the partially reflected light beam is directed towards a light intensity detector 5, where the intensity of the light beam 3 is detected. Then, the detector 5 supplies a detection signal to the driver circuit 1, thereby establishing a stabilizing feed-back loop to stabilize the light intensity of the light beam 3 to be emitted from the laser 2.
In a prior art imaging apparatus using a plurality of semiconductor lasers, such a stabilizing feed-back loop was provided for each of the lasers independently from the other. With such a structure, although the semiconductor lasers could be stabilized against changes of the surrounding temperature to the like independently, there still remained differences in characteristics among individual semiconductor lasers. For this reason, there was a limit in enhancing the quality of a resulting image using multiple of light beams. This was particularly noticeable when the prior art imaging system using a plurality of semiconductor lasers was applied to a color copier because the balance of component colors became inappropriate.